The conversion efficiency of ultra-thin solar cells based on layered materials has been limited by their open-circuit voltage, which is typically pinned to a value under 0.6 V. Here we report an open-circuit voltage of 1.02 V in a 120 nm-thick vertically stacked homojunction fabricated with substitutionally doped MoS2. This high open-circuit voltage is consistent with the band alignment in the MoS2 homojunction, which is more favourable than in widely-used TMDC heterostructures. It is also attributed to the high performance of the substitutionally doped MoS2, in particular the p-type material doped with Nb, which is demonstrated by the observation of electroluminescence from tunnelling graphene/BN/MoS2 structures in spite of the indirect nature of bulk MoS2. We find that illuminating the TMDC/metal contacts decreases the measured open-circuit voltage in MoS2 van der Waals homojunctions because they are photoactive, which points to the need of developing low-resistance, ohmic contacts to doped MoS2 in order to achieve high efficiency in practical devices. The high open-circuit voltage demonstrated here confirms the potential of layered transition-metal dichalcogenides for the development of highly efficient, ultra-thin solar cells.
@article{arxiv.2009.13911,
title = {High open-circuit voltage in transition metal dichalcogenide solar cells},
author = {Simon A. Svatek and C. Bueno and Der-Yuh Lin and James Kerfoot and Carlos Macías and Marius H. Zehender and Ignacio Tobías and Pablo García-Linares and Takashi Taniguchi and Kenji Watanabe and Peter Beton and Elisa Antolín},
journal= {arXiv preprint arXiv:2009.13911},
year = {2020}
}